Method and apparatus for scanning, stitching, and damping measurements of a double-sided metrology inspection tool

ABSTRACT

A system for inspecting specimens such as semiconductor wafers is provided. The system provides scanning of dual-sided specimens using a damping arrangement which filters unwanted acoustic and seismic vibration, including an optics arrangement which scans a first portion of the specimen and a translation or rotation arrangement for translating or rotating the specimen to a position where the optics arrangement can scan the remaining portion(s) of the specimen. The system further includes means for stitching the scans together, thereby providing both damping of the specimen and the need for smaller and less expensive optical elements.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to the field of opticalimaging and more particularly to systems for sub-aperture data imagingof double sided interferometric specimens, such as semiconductor wafers.

[0003] 2. Description of the Related Art

[0004] The progress of the semiconductor industry over the last yearshas resulted in a sharp increase in the diameters of semiconductorwafers as base material for chip production for economic and processtechnical reasons. Wafers having diameters of 200 and 300 millimetersare currently processed as a matter of course.

[0005] At present manufacturers and processors of wafers in the 200 and300 mm range do not have a wide range of measuring devices availablewhich enable inspection of particular geometric features, namelyflatness, curvature, and thickness variation, with sufficient resolutionand precision.

[0006] As scanning of specimens has improved to the sub-aperture range,the time required to perform full specimen inspection for a dual-sidedspecimen has also increased. Various inspection approaches have beenemployed, such as performing an inspection of one side of the specimen,inverting the specimen, and then inspecting the other side thereof. Sucha system requires mechanically handling the specimen, which isundesirable. Further, the act of inspecting the specimen has generallyrequired binding the specimen, which can cause deformation at the edgesof the specimen, increase defects at the edge, or cause bending of thespecimen during inspection.

[0007] One method for inspecting both sides of a dual sided specimen isdisclosed in PCT Application PCT/EP/03881 to Dieter Mueller andcurrently assigned to the KLA-Tencor Corporation, the assignee of thecurrent application. The system disclosed therein uses a phase shiftinginterferometric design which facilitates the simultaneous topographymeasurement of both sides of a specimen, such as a semiconductor wafer,as well as the thickness variation of the wafer. A simplified drawing ofthe Mueller grazing incidence interferometer design is illustrated inFIG. 1A. The system of FIG. 1A uses a collimated laser light source 101along with a lensing arrangement 102 to cause grazing of light energyoff the surface of both sides of the specimen 103 simultaneously. Asecond lensing arrangement 104 then provides focusing of the resultantlight energy and a detector 105 provides for detection of the lightenergy.

[0008] The design of FIG. 1A is highly useful in performingtopographical measurements for both sides of a dual-sided specimen in asingle measurement cycle, but suffers from particular drawbacks. First,the system requires minimum specimen movement during measurement, whichcan be difficult due to vibration in the surrounding area and vibrationof the specimen itself. Further, the inspection can be time consumingand requires highly precise light energy application and lensing, whichis expensive. The specimen must be free standing and free of edgeforces, and the incidence geometry during inspection must be unimpeded.Access must be preserved under all incidence angles. These factorsprovide mechanical challenges for successfully supporting the specimen;excessive application of force at a minimum number of points may deformthe specimen, while numerous contact points impede access and requireexact position to avoid specimen deformation or bending duringinspection. Further, edge support of the specimen has a tendency tocause the specimen to act like a membrane and induce vibration due toslight acoustic or seismic disturbances. This membrane tendency combinedwith the other problems noted above have generally been addressed byincluding most components of the system within an enclosure thatminimizes ambient vibrations, which adds significant cost to the systemand does not fully solve all vibration problems.

[0009] The cost of lenses sized to accommodate inspection of a fullwafer in the arrangement shown in FIG. 1A are highly expensive, andgenerally have the same diameter as the diameter of the specimen,generally 200 or 300 millimeters depending on the application Fullaperture decollimating optics, including precision lenses, gratings, andbeamsplitters used in a configuration for performing full inspection ofa 300 millimeter specimen are extremely expensive, generally costingorders of magnitude more than optical components half the diameter ofthe wafer.

[0010] It is therefore an object of the current invention to provide asystem for performing a single measurement cycle inspection of adual-sided specimen having dimensions up to and greater than 300millimeters.

[0011] It is a further object of the present invention to provide asystem for inspection of dual-sided specimens without requiring anexcessive number of binding points and simultaneously allowing freeaccess for inspection of both sides of the specimen.

[0012] It is a further object of the current invention to provide forthe single measurement cycle inspection of a dual-sided specimen whileminimizing the tendency for the specimen to behave as a membrane andminimize any acoustic and/or seismic vibrations associated with theinspection apparatus and process.

[0013] It is still a further object of the present invention toaccomplish all of the aforesaid objectives at a relatively low cost,particularly in connection with the collimating and decollimating opticsand any enclosures required to minimize acoustic and seismic vibrations.

SUMMARY OF THE INVENTION

[0014] The present invention is a system for inspecting a wafer,including inspecting both sides of a dual sided wafer or specimen. Thewafer is mounted using a fixed three point mounting arrangement whichholds the wafer at a relatively fixed position while simultaneouslyminimizing bending and stress. Light energy is transmitted through alensing arrangement employing lenses having diameter smaller than thespecimen, such as half the size of the specimen, arranged to cause lightenergy to strike the surface of the wafer and subsequently pass throughsecond collimating lens where detection and observation is performed.

[0015] The system further includes at least one damping bar, where thenumber of damping bars depends on the wafer repositioning arrangement.The effect of the damping bar is to perform viscous film damping, orVFD, of the non-measured surface of the specimen to minimize the effectsof vibration in accordance with VFD, or the Bernoulli principle. Eachdamping bar is positioned to be within close proximity of the surface tobe damped. The proximity between any damping bar and the surface of thewafer is preferably less than 0.5 millimeters, and spacing of 0.25 and0.33 may be successfully employed. Smaller gaps provide problems whenwarped specimens are inspected. One embodiment of the current inventionemploys a damping bar to cover slightly less than half of the specimenwhen in scanning position.

[0016] Mounting for the wafer uses a three point kinematic mount. Themounting points include clips having spherical or semi-sphericaltangentially mounted contacts, mounted to a support plate and arrangedto be substantially coplanar, where the clips are adjustable to providefor slight irregularities in the shape of the wafer. The adjustabilityof the contact points provide the ability to hold the wafer without astiff or hard connection, which could cause bending or deformation, aswell as without a loose or insecure connection, which could causeinaccurate measurements.

[0017] Light energy is conducted through a beam waveguide and thenstrikes a deviation mirror, is redirected onto a parabolic collimationmirror by two further deviation mirrors. The deviation mirrors areoriented at an angle of 90° relative to each other. The parallel lightbeam P reflected from the parabolic mirror reaches a beam splitterthrough the two deviation mirrors.

[0018] The beam splitter is formed as a first diffraction grating and isarranged in the apparatus in a vertical direction. The parallel lightbeam P strikes the diffraction grating in a perpendicular direction. Abeam collector in the form of a second diffraction grating is disposedfrom the first diffraction grating and parallel thereto. Behind the beamcollector two decollimation lenses are arranged at equal level. Thelight beams leaving the decollimation lenses are each deflected andfocused onto two CCD cameras through various deviation mirror pairs andto an optical imaging system.

[0019] The beam splitter is supported transversely to the optical axisand includes a piezoelectric actuating element for shifting the phase ofthe parallel light beam P by displacing the diffraction grating.

[0020] A wafer or specimen to be measured is held on a holding devicesuch that both plane surfaces are arranged in vertical directionparallel to the light beam P. The wafer is supported substantially atits vertical edge so that both surfaces are not substantially contactedby the support post and are freely accessible to the interferometricmeasurement.

[0021] A receiving device may be provided. Further, a referenceapparatus may be provided which comprises a reference body having atleast one plane surface. The reference body can be introduced into thelight path between the first diffraction grating and the seconddiffraction grating in place of the semiconductor wafer or specimen tobe measured by means of a traveller with a linear guide. The referencebody is held so that its plane surface is arranged in vertical directionparallel to the undiffracted light beam P.

[0022] Modifications of the imaging apparatus and method are possible. Abody having two precisely plane parallel surfaces may be used for thereference body, whereby both surfaces are measured simultaneously.However, the embodiment having a single plane surface of the referencebody is more suitable.

[0023] In one arrangement, a light source initially emits light energyand strikes two mirror surfaces, which each direct light energy througha first collimating lens and simultaneously strike the two surfaces ofthe specimen. Light energy is thereupon directed through a second pairof collimating lens and to a second pair of mirrors, toward a focusingelement arrangement, and a detector. A translation surface or mountingsurface holding the contact points and wafer or specimen is fastened toa translation stage, which provides translation or sliding of thespecimen within and into the lensing/imaging arrangement. The systemfirst performs an inspection of one portion of the specimen, and thetranslation stage and wafer are repositioned or translated such as bydriving the translating stage so that another portion of the wafer iswithin the imaging path. The other portion of the wafer is then imaged,and both two sided images of the wafer are “stitched” together.

[0024] Other means for presenting the remaining portion of wafer orspecimen may be employed, such as rotating the wafer mechanically ormanually, or keeping the wafer fixed and moving the optics and imagingcomponents. Alternately, scanning may be performed using multipletwo-sided inspections of the module, such as three, four, or five ormore scans of approximate thirds, quarters, or fifths, and so forth ofthe specimen. While multiple scans require additional time and thussuffer from increased throughput, such an implementation could providefor use of smaller optics, thereby saving overall system costs.

[0025] In a two phase scan of a dual sided specimen, at least 50 percentof the surface must be scanned in each phase of the scan. It is actuallypreferred to scan more than 50 percent, such as 55 percent, in each scanto provide for a comparison between scans and the ability to “stitch”the two scans together.

[0026] Scanning and stitching involves determining the piston and tiltof the specimen during each scan, adjusting each scan for the piston andtilt of said scan, and possibly performing an additional stitchingprocedure. Additional stitching procedures include, but are not limitedto, curve fitting the points between the overlapping portions of the twoscans using a curve fitting process, replacing overlapping pixels withthe average of both data sets, or weighting the averaging in theoverlapping region to remove edge transitions by using a trapezoidalfunction, half cosine function, or other similar mathematical function.Background references are preferably subtracted to improve the stitchingresult. If significant matching between the scans is unnecessary, suchas in the case of investigating for relatively large defects, simplycorrecting for tilt and piston may provide an acceptable result.However, in most circumstances, some type of curve fitting or scanmatching is preferred, if not entirely necessary.

[0027] These and other objects and advantages of the present inventionwill become apparent to those skilled in the art from the followingdetailed description of the invention and the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1A illustrates the general concept of the predecessor Muellersystem for inspecting both sides of a semiconductor wafer or specimenwhen said specimen is oriented in a substantially “vertical”orientation;

[0029]FIG. 1B illustrates a first embodiment of the present invention,including the damping bar and dual sided lensing arrangement;

[0030]FIG. 2 presents the mounting points of the wafer or specimen;

[0031]FIG. 3 illustrates a measurement module for use in connection withtranslating the wafer and performing multiple scans in the presence ofmultiple damping bars;

[0032]FIG. 4A shows the first position of the wafer or specimen relativeto a damping bar when a rotational scanning and stitching procedure isperformed on approximately half the wafer surface;

[0033]FIG. 4B is the second position of the wafer or specimen relativeto a damping bar when a rotational scanning and stitching procedure isperformed on the other approximately half of the wafer surface;

[0034]FIG. 5A shows the first position of the wafer or specimen relativeto a damping bar arrangement when a translational scanning and stitchingprocedure is performed on approximately half the wafer surface;

[0035]FIG. 5B is the second position of the wafer or specimen relativeto a damping bar arrangement when a translational scanning and stitchingprocedure is performed on the other approximately half of the wafersurface;

[0036]FIG. 6 represents an algorithm for performing the scanning andstitching according to the present invention;

[0037]FIG. 7 presents a conceptual schematic representation of thecomponents and optics necessary to perform dual sided imaging of asemiconductor wafer; and

[0038]FIG. 8 is a top view of the components and optics which shows thepath of light energy.

DETAILED DESCRIPTION OF THE INVENTION

[0039]FIG. 1B illustrates a first embodiment of the present invention,specifically one for scanning both sides of a dual-sided wafer orspecimen 111. According to FIG. 1B, the wafer 111 is mounted using afixed three point mounting arrangement which is shown in FIG. 2. Thethree point mounting arrangement serves to hold the wafer 111 at arelatively fixed position while simultaneously minimizing any bending orstressing of the dual-sided wafer. Light energy is transmitted throughfirst collimating lens 112 which is arranged to cause light energy tostrike the surface of the wafer 111 and subsequently pass through secondcollimating lens 113 where detection and observation is performed. Asmay be appreciated by examining FIG. 1B, the diameter of both firstcollimating lens 112 and second collimating lens 113 are significantlysmaller than the diameter of the specimen or wafer 111, and incidentlight strikes only a portion of the surface of wafer 111. Not shown inthe illustration of FIG. 1B is that while light energy is striking thesurface of wafer 111 visible in the arrangement shown, light energysimultaneously passes through first collimating lens 112 and strikes thereverse side of the wafer 111, not shown in FIG. 1B. Light energy passesfrom the reverse side of the specimen 111 through second collimatinglens 113.

[0040] The arrangement further includes an upper damping bar 114 and alower damping bar 115. In the arrangement shown in FIG. 1B, the upperdamping bar 114 covers approximately one half of the specimen 111,specifically the half not being inspected. The effect of the damping baris to damp the non-measured surface of the specimen 111 to minimize theeffects of vibration. Damping in this arrangement is based on VFD, orthe Bernoulli principle, wherein the upper damping bar 114 in thearrangement shown is brought to within close proximity of the surface tobe damped. The proximity between either damping bar 114 or 115 and thesurface of the wafer is preferably less than 0.5 millimeters, andspacing of 0.25 and 0.33 may be successfully employed. The problemassociated with providing smaller gaps between either damping bar 114 or115 and the surface of wafer 111 is that any warping of the wafer maycause the bar to contact the surface. For this reason, and depending onthe wafer surface, gaps less than 0.10 millimeters are generallyundesirable. Further, gaps greater than 1.0 millimeters do not produce adesirable damping effect, as the Bernoulli principle does not result insufficient damping in the presence of gaps in excess of 1.0 millimeter.

[0041] The gap between the specimen 111 and upper damping bar 114 orlower damping bar 115 restricts airflow between the specimen and thedamping bar and damps vibration induced in the specimen. Each dampingbar is generally constructed of a stiff and heavy material, such as asolid steel member. Overall dimensions are important but not critical inthat the damping bar should cover a not insignificant portion of thewafer 111. Coverage of less than 20 percent of the wafer tends tominimize the overall damping effect on the wafer, but does provide somelevel of damping.

[0042] The illumination of only a portion of the wafer 111 provides forusing smaller lenses than previously performed. In the embodiment shownin FIG. 1B, the preferred size of the first collimating lens 112 andsecond collimating lens 113 is approximately 4.4 inches where the wafer111 is 300 millimeters in diameter. In such an arrangement, the dampingbars 114 and 115 are approximately 4.5 inches wide. Length of thedamping bars depends on the mode of wafer movement, as discussed below.

[0043] As shown in FIG. 2, the mounting for the wafer 111 is preferablyusing a three point kinematic mount, where the three points 201, 202,and 203 represent spherical or semispherical contacts tangential to oneanother. Points 201, 202, and 203 are small clips having spherical orsemi-spherical tangentially mounted contacts, mounted to a support platesuch as mounting plate 116 to be substantially coplanar, with adjustableclips to provide for slight irregularities in the shape of the wafer111. The spherical or semispherical components should be sufficientlyrigid but not excessively so, and a preferred material for thesecomponents is ruby. The adjustability of points 201, 202, and 203provide an ability to hold the wafer 111 without a stiff or hardconnection, which could cause bending or deformation, as well as withouta loose or insecure connection, which could cause inaccuratemeasurements. In FIG. 1B, two lower kinematic mount points 202 and 203(not shown) support the lower portion of the wafer 111, while the upperportion is supported by mount point and clip 201. The points 201, 202and 203 are therefore stiff enough to mount the wafer or specimen 111and prevent “rattling” but not so stiff as to distort the wafer. Thespherical or semispherical contact points are generally known to thoseof skill in the mechanical arts, particularly those familiar withmounting and retaining semiconductor wafers. The combination of clampingin this manner with the Bernoulli damping performed by the damping bars114 and 115 serves to minimize acoustic and seismic vibration.

[0044] Simultaneous imaging of both sides of the specimen is performedin accordance with PCT Application PCT/EP/03881 to Dieter Mueller,currently assigned to the KLA-Tencor Corporation, the assignee of thecurrent application. The entirety of PCT/EP/03881 is incorporated hereinby reference. This imaging arrangement is illustrated in FIGS. 7 and 8.As shown in FIGS. 7 and 8, the light energy directing apparatus employedin the current invention comprises a light source in the form of a laser801. The light emitted from the laser 801 is conducted through a beamwaveguide 802. The light produced by the laser 801 emerges at an end 803of the beam waveguides 802 so that the end 803 acts as a punctual lightsource. The emerging light strikes a deviation mirror 804 wherefrom itis redirected onto a collimation mirror 807 in the form of a parabolicmirror by two further deviation mirrors 805 and 806. Deviation mirrors805 and 806 are oriented at an angle of 90° relative to each other; Theparallel light beam P reflected from the parabolic mirror 807 reaches abeam splitter 808 through the two deviation mirrors 805 and 806.

[0045] The beam splitter 808 is formed as a first diffraction gratingand is preferably a phase grid. The beam splitter 808 is arranged in theapparatus in a vertical direction and the parallel light beam P strikesthe diffraction grating in a perpendicular direction. A beam collector810 in the form of a second diffraction grating is disposed from thefirst diffraction grating 808 and parallel thereto. Behind the beamcollector 810 two decollimation lenses 811 are arranged at equal leveland the light beams leaving these decollimation lenses are eachdeflected and focused onto two CCD cameras 816, through deviation mirrorpairs 812A and 812B, 813A and 813B, and 814A and 814B, and to an opticalimaging system 15.

[0046] The beam splitter 808 is supported transversely to the opticalaxis and further comprises a piezoelectric actuating element 817 forshifting the phase of the parallel light beam P by displacing thediffraction grating.

[0047] A holding device 830, for example in the form of a support post,is provided centrally between the first diffraction grating and thesecond diffraction grating. A wafer or specimen 809 to be measured isheld on the holding device 830 such that both plane surfaces 831 and 832are arranged in vertical direction parallel to the light beam P. Thewafer 809 is supported by the support post substantially at its verticaledge 833 only so that both surfaces 831 and 832 are not substantiallycontacted by the support post and are freely accessible to theinterferometric measurement.

[0048] Moreover, a receiving device (830, 825) may be provided for thewafer 809 to be measured. The wafer can be inserted into the receivingdevice in a horizontal position. By means of a tilting device 826 thewafer 809 may be tilted from its horizontal position into the verticalmeasuring position, and the wafer 809 may be transferred, by means of apositionable traveller, into the light path between the firstdiffraction grating and the second diffraction grating so that thesurfaces 809 and 832 to be measured are aligned substantially parallelto the undiffracted light beam P and in a substantially verticaldirection.

[0049] Furthermore, a reference apparatus 820 may be provided whichcomprises a reference body 821 having at least one plane surface 824.The reference body 821 can be introduced into the light path between thefirst diffraction grating 808 and the second diffraction grating 810 inplace of the semiconductor wafer or specimen 809 to be measured by meansof a traveller 823 with a linear guide 818. The reference body 821 isheld so that its plane surface 824 is arranged in vertical directionparallel to the undiffracted light beam P. The reference body 821 can beturned by 180° in its mounting around an axis parallel to its surface824.

[0050] In operation the wafer or specimen 809 to be measured is firstinserted into the wafer receiving device 825. The surfaces 831 and 832are horizontally arranged. By means of the tilting device and of thetraveller 819 the wafer to be measured is brought into the holdingdevice 830 where it is arranged so that the surfaces 831 and 832 arevertical. A diffraction of the parallel light beam P striking the firstdiffraction grating 808 of the beam splitter produces partial lightbeams A, B, whereby the partial light beam A having a positivediffraction angle strikes the one surface 831 of the wafer 809 and isreflected thereat, whereas the partial light beam B with a negativediffraction angle strikes the other surface 832 of the wafer and isreflected thereat. The 0-th diffraction order of the parallel light beamP passes through the first diffraction grating 808 and is not reflectedat the surfaces 831 and 832 of the wafer 809. This partial light beam Pserves as references beam for interference with the reflected wavefronts of the beams A and B. In the second diffraction grating 810, thebeam collector and the reflected partial light beams A and B are eachcombined again with the reference beam P of the 0-th diffraction orderand focused, in the form of two partial light beams A+P and B+P onto thefocal planes of the CCD cameras 816 through decollimation lenses 811 anddeviation mirrors 812, 813 and 814 as well as positive lenses 815.

[0051] During the exposure of the surfaces the phase of the parallellight beam P is repeatedly shifted by 90° and 120° by displacing thediffraction grating. This produces phase shifted interference patterns.The defined shift of the interference phase produced by the phaseshifter 817 is evaluated to determine whether there is a protuberance ora depression in the measured surfaces 831 and 832 the two digitizedphase patterns are subtracted from each other.

[0052] A calibration using the reference body 821 can be performedbefore each measurement of a wafer 809. The reference body 821 isintroduced into the beam path between the first diffraction grating 808and the second diffraction grating 810. The known plane surface 824 ismeasured. Subsequently the reference body 821 is turned by 180° and thesame surface 824 is measured as a second surface.

[0053]FIG. 3 illustrates the measurement model without a wafer orspecimen present. From FIG. 3, light source 301 initially emits lightenergy and is focused to strike first mirror surface 302 and secondmirror surface 303 (not shown). Each of these two mirror surfaces directlight energy through first collimating lens 112 (not shown in this view)and light energy strikes the two surfaces of specimen 111 (also notshown) simultaneously. After striking the two surfaces of specimen 111,light energy is directed through second collimating lens 113 (also notshown in FIG. 2) and to third mirror 304 and fourth mirror 305, whichdirect light energy toward focusing element 306 and detector 307.Imaging arm 311 represents the light image path from third mirror 304toward focusing element 306. Focusing elements and sensors are thoseknown in the art, and may include a lensing arrangement, such asmultiple lenses, and a CCD or other imaging sensor. Otherimplementations of focusing element 306 and detector or sensor 307 arepossible while still within the scope of the current invention.

[0054] From FIG. 1B, the specimen 111 is mounted to three points,including point 201, which are fixedly mounted to mounting surface 116.Mounting surface 116 may be fixedly mounted to translation surface 117.Either translation surface 117 or mounting surface 116 is fastened totranslation stage 308, which provides translation or sliding of themounting surface 116 and specimen 111 within and into the arrangementshown in FIG. 3. The arrangement may further include translation surface117 depending on the application. Translation stage 308 permits thearrangement of FIG. 1B, specifically wafer or specimen 111, points 201,202, and 203, mounting surface 116, and translation surface 117, to moveup and down in a relatively limited range, as described below. In suchan arrangement employing translation surface 117, the translationsurface and the mounting surface along with the contact points arepositioned within the measurement module 300, preferably by affixing thetranslation surface 117 to the translation stage 308. Specimen 111 isthen physically located between damping bars 114 and 115, as well asproximate damping bar 309 and fastened to points 201, 202, and 203. Oncethe specimen 111 has been adequately fastened to points 201, 202, and203, an inspection of the lower portion of the wafer is initiated. Aftercompleting an adequate inspection, i.e. an inspection of one portion ofthe specimen 111 with acceptable results, the translation stage 308 andultimately the wafer are repositioned or translated such as by drivingthe translating stage 308 along track 310 such,that another portion ofthe wafer 111, such as the remaining approximately half of specimen 111is within the imaging path. The other portion of the wafer is thenimaged, and both of the two sided images of the wafer surface are“stitched” together.

[0055] The damping bars may have varying size while still within thescope of the current invention, as discussed above. In FIG. 3, thedamping bars are affixed to end pieces 310 and 311, but any type ofmounting will suffice as long as the gap spacing described above and theability to perform scans on desired portions of the wafer is available.

[0056] As may be appreciated, other means for presenting the remainingportion of wafer or specimen 111 may be employed, such as rotating thewafer by hand by releasing contact with the points and rotating thewafer manually. Alternately, a mechanical rotation of the specimen mayoccur, such as by rotatably mounting the mounting surface 116 on thetranslating surface 117 while providing for two locking positions forthe mounting surface 116. In other words, the arrangement of wafer 111,points 201, 202, and 203, and mounting surface 116 would initiallyfixedly engage translation surface 117. On completion of a firstinspection scan of a portion of specimen 111, wafer 111, points 201,202, and 203, and mounting surface 116 would be unlocked fromtranslation surface 117 and be mechanically or manually rotatedvertically on an axis perpendicular to translation surface 117. Thewafer and associated hardware rotate 180 degrees to a second lockingposition, wherein the surface would lock and a second inspection scanwould commence. During this rotation scheme, damping bars andimpediments would be mechanically or manually removed to prevent contactwith mounting points 201, 202, and 203. The various components,particularly mounting surface 116, are sized to accommodate rotationwithin the measurement module 300 without contacting the translationstage or other module components.

[0057] Alternately, scanning may be performed using multiple two-sidedinspections of the module, such as three, four, or five scans ofapproximate thirds, quarters, or fifths of the specimen. While multiplescans require additional time and thus suffer from increased throughput,such an implementation could provide for use of smaller optics, therebysaving on system costs. Numerous sub-aperture scans may be performed bya system similar to that illustrated in FIG. 3 while still within thescope of the current invention.

[0058]FIGS. 4A and 4B illustrate a rotational scanning arrangement ofthe wafer or specimen 111. As may be appreciated, in a two phase scan ofa dual sided specimen, at least 50 percent of the surface must bescanned in each phase of the scan. It is actually preferred to scan morethan 50 percent, such as 55 percent, in each scan to provide for acomparison between scans and the ability to “stitch” the two scanstogether. In such an arrangement, as shown in FIG. 4A, over 50 percentof the surface is scanned initially, shown as portion A of the surface111. Portion B is obscured by one of the damping bars. After the initialscan phase, the specimen 111 is rotated manually or mechanically to theposition illustrated in FIG. 4B. Approximately 55 percent of the wafersurface, both front and back, are scanned during this second phase. Thisprovides an overlap of five percent of the wafer, and comparisonsbetween these overlap portions provides a reference for stitching thescans together. In FIG. 4B, the A portion of the wafer is obscured bythe damping bar.

[0059] Alternately, as in the arrangement shown in FIG. 3, the wafer orspecimen 111 may be translated vertically and two or more separate scansperformed. As shown in FIGS., 5A and 5B, a portion of the wafer 111 ispositioned between two damping bars, such as damping bars 114 and 115,and the portion marked “B” in FIG. 5A is scanned. As shown therein,greater than 50 percent of the specimen 111 is scanned so that theoverlapping portion may be stitched with the second scan. After theinitial scan, the wafer is translated to a position as shown in FIG. 5B.Portion “A” of FIG. 5B is then scanned, while the lower damping barcovers much of section “B.” The overlapping portions of the two scansare then stitched together to provide a full representation of thesurface, and again such a scan is dual-sided.

[0060] From FIGS. 4A, 4B, 5A, and 5B, it should be apparent that asingle damping bar is required if the specimen 111 is to be rotated asshown in FIGS. 4A and 4B, while two damping bars are required if thewafer 111 is to be translated, as shown in FIGS. 5A and 5B. Note thatdue to measurement setup, an arbitrary piston or DC offset and tilt willbe applied to each of the measurements, indicating that some correctionis required prior to or during stitching to obtain an accurate surfacerepresentation.

[0061]FIG. 6 illustrates a general scanning and stitching algorithm foruse in accordance with the invention described herein. The algorithmbegins in step 601 and performs the first scan in step 602, as well asdetermining the piston and tilt of the specimen 111. The algorithmevaluates whether the scan is acceptable in step 603, either performedby an operator actually evaluating the scan or a mechanical comparisonwith a known or previous scan. If the scan is acceptable, the algorithmproceeds to step 604 where the wafer is repositioned to the nextlocation. If the scan is not acceptable, the wafer is rescanned in itsoriginal position. Piston and tilt may be recomputed, but as the waferhas not moved this is not necessary. Once the wafer has beenrepositioned in step 604, a subsequent scan is performed in step 605 andthe tilt and piston computed for the new orientation. The acceptabilityof the scan is evaluated in step 606, and if unacceptable, the scan,performed again. The piston and tilt again do not need to berecalculated. Once the scan is mechanically or visually deemedacceptable, the algorithm determines whether the entire surface has beenscanned in step 607. If the entire surface has not been scanned, thewafer is again repositioned and the remaining scans performed inaccordance with the illustrated steps. If the entire surface has beenscanned, the algorithm sets x equal to one and y equal to 2 in step 608.In step 609 the system alters scan x for tilt and piston and separatelyalters scan y for. its respective tilt and piston. At this point scans xand y are neutrally positioned and may be stitched together. Step 610 isan optional step of performing an additional stitching procedure.Additional stitching procedures include, but are not limited to, curvefitting the points between the overlapping portions of the two scansusing a curve fitting process, replacing overlapping pixels with theaverage of both data sets, or weighting the averaging in the overlappingregion to remove edge transitions by using a trapezoidal function, halfcosine function, or other similar mathematical function. Backgroundreferences are preferably subtracted to improve the stitching result. Ifsignificant matching between the scans is unnecessary, such as in thecase of investigating for relatively large defects, simply correctingfor tilt and piston may provide an acceptable result, and. step 610 neednot be performed. However, in most circumstances, some type of curvefitting or scan matching is necessary. Scans are matched and stitched instep 611. Such stitching algorithms should preferably be performed usinga computing device, such as a microprocessor (not shown).

[0062] Step 612 evaluates whether the complete wafer has been stitchedtogether. If it has not, the algorithm proceeds to increment x and y instep 613 and perform additional stitching of the remaining portions. Ifthe complete wafer has been stitched, the algorithm exits in step 614.

[0063] Based on the disclosure presented above and in particular inconnection with that shown in FIG. 3, the wafer 111 is generallyrepositioned while the inspection energy source and optics remain fixed.While this implementation provides distinct advantages in setup time forperforming multiple dual-sided wafer scans, it is to be understood thatthe light source and associated optics and detector may be slidably orrotationally mounted while the wafer remains fixed. In the configurationillustrated in FIG. 3, source 301, support elements 310 and 311, dampingbars 114 and 115, damping bar 309, the four mirrors 302, 303, 304, and305, focusing element 306, and detector 307 may be mounted to a singlesurface and fixedly positioned relative to one another, and translatedor rotated about the wafer. Alternately, the components may betranslated either together or individually to perform subsequent scansof the wafer or specimen 111.

[0064] While the invention has been described in connection withspecific embodiments thereof, it will be understood that the inventionis capable of further modifications. This application is intended tocover any variations, uses or adaptations of the invention following, ingeneral, the principles of the invention, and including such departuresfrom the present disclosure as come within known and customary practicewithin the art to which the invention pertains.

What is claimed is:
 1. A system for scanning both sides of a two sidedspecimen, comprising: means for maintaining said specimen in asubstantially fixed position; means for damping said specimen; means forperforming a plurality of scans on predetermined portions of saidspecimen; means for repositioning said specimen relative to saidperforming means; and means for stitching all scans to form a relativelycontinuous scan of each side of said two sided specimen.
 2. The systemof claim 1, wherein said damping means comprise at least one damping barpositioned approximately 0.10 to 1.0 millimeters from said specimen. 3.The system of claim 1, wherein said repositioning means comprises meansfor translating said specimen and said performing means comprises aninspection arrangement wherein said inspection arrangement scans apredetermined portion of said specimen unobstructed by said dampingmeans.
 4. The system of claim 1, wherein said maintaining meanscomprises a three point kinematic mount, wherein all points of saidthree point kinematic mount are tangentially mounted, and wherein saidspecimen is a substantially vertically mounted semiconductor wafer. 5.The system of claim 1, wherein said stitching means comprises a computerfor substantially uniformly orienting said scans and combining saidscans.
 6. A method for scanning a specimen, comprising the steps of:maintaining said specimen in a substantially fixed position; dampingsaid specimen; performing a first scan on a first predetermined portionof said specimen using a scanning apparatus; repositioning said specimenrelative to said scanning apparatus; performing at least one subsequentscan on at least one subsequent predetermined portion of said specimen;and stitching all scans to form a relatively continuous scan of saidspecimen.
 7. The method of claim 6, wherein damping is performed bypositioning at least one damping bar approximately 0.10 to 1.0millimeters from said specimen.
 8. The method of claim 7, wherein:repositioning comprises translating said specimen; and each performingstep comprises scanning a portion of said specimen unobstructed by anydamping bar.
 9. The method of claim 6, wherein maintaining comprisesholding said specimen using a three point kinematic mount in asubstantially vertical on-edge type orientation.
 10. The method of claim6, wherein stitching comprises substantially uniformly orienting saidscans and combining said scans.
 11. A system for scanning a specimen,comprising: a positioning arrangement to fixedly maintain said specimenin a predetermined position; scanning optics to direct light energy to asurface of said specimen; a repositioning element for relativelyrepositioning said positioning arrangement with said scanning optics; atleast one damping element proximately located to said specimen; and astitching device to stitch scans obtained from said scanning optics. 12.The system of claim 11, wherein each damping element comprises at leastone damping bar positioned approximately 0.10 to 1.0 millimeters fromsaid specimen.
 13. The system of claim 11, wherein said repositioningelement comprises translating means for translating said specimen andsaid scanning optics scan a predetermined portion of said specimenunobstructed by said damping element.
 14. The system of claim 11,wherein said maintaining means comprises a three point kinematic mount,wherein all points of said three point kinematic mount are tangentiallymounted, and wherein said specimen is a substantially vertically mountedsemiconductor wafer.
 15. The system of claim 11, wherein said stitchingdevice comprises a computer for substantially uniformly matching theorientation of said scans and combining said scans.
 16. A method forscanning a specimen, comprising: positioning said specimen in arelatively fixed position; damping said specimen; scanning a pluralityof portions of said specimen; and stitching said portions together. 17.The method of claim 16, wherein damping is performed by positioning atleast one damping bar approximately 0.10 to 1.0 millimeters from saidspecimen.
 18. The method of claim 17, wherein performing comprisesscanning a portion of said specimen unobstructed by any damping bar. 19.The method of claim 16, wherein maintaining comprises holding saidspecimen using a three point kinematic mount in a substantially verticalon-edge type orientation.
 20. The method of claim 16, wherein stitchingcomprises substantially uniformly orienting said scans and combiningsaid scans.